1. Field of the Invention
The present invention relates to a non-contact type transmission device for use in an information recording apparatus, e.g., a video tape recorder and to a rotary magnetic head unit having the non-contact type transmission device.
2. Description of the Related Art
Video tape recorders, tape streamers and so on are known as apparatuses for recording information on a magnetic tape and for reproducing information from the magnetic tape. An information recording apparatus of this kind has a rotary magnetic head unit for a recording signal on a magnetic tape and for reproducing a signal recorded on a magnetic tape.
The rotary magnetic head unit has a rotating drum and a fixed drum. The rotating drum has a recording head and a reproducing head. The recording head is a head for recording a signal on a magnetic tape, and the reproducing head is used to reproduce a signal recorded on a magnetic tape.
The rotating drum holds the recording head and the reproducing head and rotates relative to the fixed drum by the operation of a motor to scan a magnetic tape with the recording head or the reproducing head by, for example, the helical scanning method, thereby recording information on the magnetic tape or reproducing information from the magnetic head.
If such a helical scanning system is used, signals can be recorded on a magnetic tape at a high density and the relative speed between the magnetic tape and the magnetic head can be increased.
The helical scanning type rotary magnetic head unit needs to transmit signals and electric power between the rotating drum and the fixed drum in a non-contact manner since the recording head and the reproducing head are accommodated in the rotating drum. For example, there is a need to transmit a reproduction signal, which is obtained by the reproducing head, from the rotating drum side to the fixed drum side in a non-contact manner, and to supply electric power from the fixed drum side to a circuit board provided on the rotating drum side.
Conventional rotary magnetic head units of this kind use a rotary transformer for a non-contact signal transmission system only and require another rotary transformer for power supply if non-contact power supply is necessary. A signal system rotary transformer and a power supply rotary transformer are separately provided in such conventional magnetic head units in order to prevent crosstalk of a transmitted signal used with the power supply rotary transformer to the signal system rotary transformer.
This "crosstalk" is a leak of a signal through a leakage magnetic field between adjacent signal and power supply systems or between different signal systems.
Rotary magnetic head units having two rotary transformers, however, are large in size and high in manufacturing cost. Also, it is technically difficult to incorporate two rotary transformers in a small rotary magnetic head unit.
A magnetoresistive element head (MR head) is used as a head for reproducing information recorded on a magnetic recording medium. A reproducing magnetoresistive element head constantly requires a bias current when operated to obtain a reproduction signal. A magnetoresistive element head is a head in which a change in resistance is caused by a change in magnetic field, and in which a change in signal magnetic field (input signal) is converted into a change in resistance to be extracted as a change in reproduction output signal.
Such a magnetoresistive element head can be used advantageously as a reproducing head because of its ability to obtain a stable reproduction output signal independent of the magnetic tape speed.
In using a reproducing magnetoresistive element head of this kind by causing a bias current to flow continuously therethrough during reproduction, there is a problem relating to wear of the magnetoresistive element head. That is, as the total of time periods through which a magnetoresistive element head is operated to reproduce signals from magnetic tapes, the amount of wear of the head increases inevitably. With wear of the head, a change occurs in signal reproduction characteristics of the magnetoresistive element head. A suitable reproduction output signal cannot be obtained unless the bias current is changed according to wear of the head.